A patent foramen ovale is a persistent, one-way, usually flap-like opening in the wall between the right atrium and left atrium of the heart. In utero, the foramen ovale serves as a physiologic conduit for right-to-left shunting of blood in the fetal heart. Because blood is oxygenated through the umbilical chord, and not through the developing lungs, the circulatory system of the fetal heart allows the blood to flow through the foramen ovale as a physiologic conduit for right-to-left shunting. After birth, with the establishment of pulmonary circulation, the increased left atrial blood flow and pressure presses the septum primum against the walls of the septum secundum, covering the foramen ovale and resulting in functional closure of the foramen ovale. This closure is usually followed by anatomical closure of the foramen ovale due to fusion of the septum primum to the septum secundum.
Where anatomical closure of the foramen ovale does not occur, a PFO is created. Studies have shown that a relatively large percentage of adults have a PFO. The presence of a PFO is generally considered to have no therapeutic consequence in otherwise healthy adults. Because left atrial (LA) pressure is normally higher than right atrial (RA) pressure, the flap usually stays closed. Under certain conditions, however, right atrial pressure can exceed left atrial pressure, creating the possibility that blood could pass from the right atrium to the left atrium and blood clots could enter the systemic circulation. It is desirable that this circumstance be eliminated.
Paradoxical embolism via a PFO is considered in the diagnosis for patients who have suffered a stroke or transient ischemic attack (TIA) in the presence of a PFO and without another identified cause of ischemic stroke. While there is currently no definitive proof of a cause-effect relationship, many studies have confirmed a strong association between the presence of a PFO and the risk for paradoxical embolism or stroke. It has been estimated that in 50% of cryptogenic strokes, a PFO is present. In addition, there is significant evidence that patients with a PFO who have had a cerebral vascular event are at increased risk for future, recurrent cerebrovascular events.
Patients suffering a cryptogenic stroke or a transient ischemic attack (TIA) in the presence of a PFO often are considered for medical therapy to reduce the risk of a recurrent embolic event. Accordingly, patients at such an increased risk are considered for prophylactic medical therapy to reduce the risk of a recurrent embolic event. These patients are commonly treated with oral anticoagulants to reduce the risk of a recurrent embolic event. However, these anticoagulants have potentially adverse side effects, including hemorrhaging, hematoma, and adverse interactions with other drugs. In addition, use of anticoagulant drugs can alter a person's recovery and necessitate adjustments in a person's daily living pattern.
Where anticoagulation is contraindicated, surgery may be employed to close a PFO. The surgery would typically include suturing a PFO closed by attaching septum secundum to septum primum. Like other open surgical treatments, however, this surgery is highly invasive, risky, requires general anesthesia, and may result in lengthy recuperation.
Nonsurgical closure of PFOs has become possible with the introduction various mechanical closure devices, including umbrella devices and the like, which were initially for percutaneous closure of atrial septal defects (ASDs; a condition where there is not a septum primum). These devices potentially allow patients to avoid the side effects often associated with anticoagulation therapies and the risks of invasive surgery.
However, devices for treating heart defects, such as PFO and other atrial and ventricular septal heart defects have their share of drawbacks. The complex anatomical features of PFOs present a challenge to a one size fits all approach. The PFO involves two components, septum primum and septum secundum. The septum secundum is thicker than septum primum and exhibits limited mobility and compliance. Failure of these two structures to fuse creates a tunnel-like opening, the PFO. The distance of the nonfusion between the two septa determines the particular size of the PFO, which must be considered in the design of a device targeting PFOs. Nevertheless, devices are often configured so that the patient's anatomy must be adjusted to fit the geometry of the device. As a consequence, heart tissue may be torn when accommodating such devices.
Conventional nonsurgical closure devices are often technically complex, bulky, have a high septal profile, low radiopacity, and an inability to provide immediate closure. Additionally, many of the devices have a geometry which tends to prevent the device from remaining flat against, or within the defect once deployed. The varying passageway geometries often require multiple sized devices. Moreover, many devices are set apart by a relatively long central section corresponding to the PFO tunnel. By increasing the device profile, the device can present difficulties with respect to complete endothelialization. Conventional closure devices are often difficult to deploy or reposition, often require replacement or repositioning, and require relatively large delivery catheters (for example, 9-10 French or more). In addition, the large masses of foreign material associated with the device may lead to unfavorable body adaptation to the device, including thromboses or other unfavorable reactions. Further drawbacks to nonsurgical closure devices include complications resulting from fractures of the components, conduction system disturbances, perforations of heart tissue, residual leaks, and inability to allow subsequent methods involving transeptal puncturing.
Accordingly, there is a need for improved low profile closure devices and simplified delivery methods for immediate closure, which are capable of limiting the amount of foreign material deployed and enhancing closure stability. The present invention is designed to address a number of the deficiencies surrounding conventional closure devices.